A circuit board, such as a main board or a mother board, typically has a plurality of electronic components, such as a central processing unit or a graphic card, provided thereon, and conductive circuits that electrically connect the electronic components. The electronic components generate heat during operations, and if the heat generated is not dissipated from an electronic product in which the circuit board is provided, the electronic components may be overheated and fail. Such a problem becomes more prominent in the face of increasing demands for functions and processing speeds, because enhancement in the functions and processing speeds of the circuit boards means that the electronic components integrated on the circuit boards will need to be more or higher end. More or higher end electronic devices generate more heat. Therefore, effectively dissipating the heat generated from the circuit board is a necessary design consideration.
One of the approaches to dissipate heat that is commonly used in the industry involves installing a cooling fan on the main board or the mother board to dissipate the heat generated by the electronic devices. This kind of cooling fan can be seen in U.S. Pat. Nos. 6,799,282, 7,215,548, 7,286,357 and 7,568,517, for example.
As an example, a conventional heat dissipating device 1 shown in FIG. 1A is installed on a predetermined location of a circuit board, and comprises a printed circuit board 11, a housing 12 and a fan wheel set 13. The housing 12 has a base 120, a shaft sleeve 122 and a stator set 121 disposed around the shaft sleeve 122. The fan wheel set 13 has a hub 130, a magnet 131 located on an inner side of the hub 130, a plurality of blades 132 disposed around a periphery of the hub 130, and an shaft member 133 pivotally connected to the hub 130 and pivotally disposed in the shaft sleeve 122. The printed circuit board 11 has at least one control chip 110 and a plurality of passive elements 112 provided thereon. The printed circuit board 11 is disposed on the base 12 of the housing 120 to control the rotation of the fan wheel set 13 via the control chip 110, so that the rotation of the fan wheel set 13 can drive airflow.
The control chip 110 used in the conventional heat dissipating device 1 shown in FIG. 1A is a heat source. If heat generated by the control chip 10 cannot escape, it may lead to overheating and failing of the chip itself, which in turn will lead to the standstill of the fan wheel set 13. Thus, the heat generated by the electronic components on the main board of the electronic product cannot be dissipated effectively, resulting in failing or even damage of the electronic product. The control chip 110 is located just in a gap between the base 120 of the housing 12 and the hub 130 of the fan wheel set 13. The narrow gap often results in ineffective dissipation of the heat generated by the control chip 110, leading to overheating and damage of the control chip 110. The heat dissipating device 1 is a relative cheap component among the various components of the electronic product. However, if the heat dissipating device 1 cannot operate properly, it will damage the more expensive core component (the main board) of the electronic product, so its importance cannot be measured in terms of its price.
In addition, the provision of the control chip 110 will influence the size of the gap between the hub 130 of the fan wheel set 13 and the base 120 of the housing 12. An increase in the thickness of the control chip 110 very often requires an increase in the width of the gap, which is detrimental to the reduction of the overall height of the heat dissipating device 1. Moreover, the provision of the control chip 110 increases the footprint of the printed circuit board 11. If the area of the printed circuit board 11 is increased without increasing the cross-sectional area of this type of conventional heat dissipating device 1, then the area of the blades 132 will need to be reduced. However, a reduction in the area of the blades 132 will influence the airflow output. A lack of airflow output will affect the desired effect of heat dissipation.
In order to solve the problems, U.S. Pat. No. 7,345,884 proposed an improved cooling fan. As shown in FIG. 1B, the structure of a cooling fan 1′ described in U.S. Pat. No. 7,345,884 is substantially the same as the structure of the prior art mentioned above. The difference is in that the printed circuit board 11′ is formed with an extending part 11a that extends outwardly to allow the control chip 110′ to be provided thereon, such that the control chip 110′ is located entirely or partially outside the gap between the base 120′ of the housing 12′ and the hub 130′ of the fan wheel set 13′. As such, the heat generated by the control chip 110′ can be effectively removed by the airflow driven by the fan wheel set 13′.
However, the formation of the above outward extending part 11a of the printed circuit board 11′ will interfere the airflow driven by the rotation of the fan wheel set 13′. Interfered airflow will generate noise, which in turn degrades the quality of the electronic product equipped with such kind of cooling fan 1′. Meanwhile, due to the outward extension of the extending part 11a, certain interval has to be kept between the blades 132′ and the control chip 110′. This is also unfavorable to the reduction of the overall height of the conventional cooling fan 1′, therefore failing to satisfy the needs for thinner electronic products.
Furthermore, the conventional cooling fan 1′ still requires the printed circuit board 11′ to be provided between the hub 130′ of the fan wheel set 13′ and the base 120′ of the housing 12′, so the thickness of the printed circuit board 11′ will still affect the overall height of the cooling fan 1′, which makes further thinning of the cooling fan 1′ more difficult.
Therefore, overcoming aforementioned prior art problems is the current objective to be addressed.